In order to use an integrated circuit chip, it is necessary to make electrical connection to the integrated circuit incorporated within the chip. These connections are made through contact pads located at one main face (hereinafter called the interconnect face) of the chip. Frequently, it is desired to mount the chip on an etched circuit board (ECB) and to establish electrical connection between the contact pads of the chip and circuit runs of the ECB, so as to connect the integrated circuit to other components mounted on the ECB.
As integrated circuits become more complex, in terms of both number of connections (i.e., the number of contact pads) and density of connections (i.e., the ratio of the number of connections to the area available for the connections), it is increasingly necessary to pay attention to factors other than the ohmic performance of the connections between the chip and the circuit board. For example, one reason for seeking to incorporate integrated circuits in ever smaller chips (and consequently increasing the density of connections) is in order to keep internal path lengths short and avoid degradation of high frequency signals. At high signal frequencies, severe demands are placed on the interconnections between the chip and the circuit board in order to avoid unacceptable degradation of the signal.
One electrical connector that is able to transmit high frequency signals without undue degradation is described in U.S. Pat. No. 4,255,003 issued March 10, 1981. In the case of that connector, the chip is mounted on a ceramic substrate that has conductor runs extending from the contact pads of the chip to the periphery of the substrate. The substrate is fitted in a recess in the circuit board, and the conductor runs at the periphery of the substrate align with corresponding conductor runs on the upper surface of the board. A frame-like pressure pad of elastomer, having conductive fingers on its lower surface, is fitted so that it bridges the gap between the ceramic substrate and the circuit board and the conductive fingers establish connection between the conductor runs of the substrate and the corresponding conductor runs of the circuit board. A frame member is fitted over the pressure pad and is secured to the board, compressing the elastomer so that contact force is provided for maintaining the conductive fingers in contact with the conductor runs. This type of connector has been used successfully with signals at frequencies up to 10 GHz.
It is also known to make connections to a chip mounted on a ceramic substrate by use of a lead frame. The lead frame comprises a sheet of metal having four side regions surrounding a rectangular opening, and discrete leads extending, like teeth of a comb, from the side regions towards the center of the opening. The inner ends of the leads are attached to the contact pads of the substrate, and the leads are then electrically isolated from one another by removing the side regions.